Implant tool and improved electrode design for minimally invasive procedure

ABSTRACT

Devices and methods of use for introduction and implantation of an electrode as part of a minimally invasive technique. An implantable baroreflex activation system includes a control system having an implantable housing, an electrical lead, attachable to the control system, and an electrode structure. The electrode structure is near one end of the electrical lead, and includes a monopolar electrode, a backing material having an effective surface area larger than the electrode, and a releasable pivotable interface to mate with an implant tool. The electrode is configured for implantation on an outer surface of a blood vessel and the control system is programmed to deliver a baroreflex therapy via the monopolar electrode to a baroreceptor within a wall of the blood vessel.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 15/251,239filed Aug. 30, 2016 and now issued as U.S. Pat. No. 10,350,406, which isa continuation of application Ser. No. 14/319,770 filed Jun. 30, 2014and now issued as U.S. Pat. No. 9,511,218, which is a continuation ofapplication Ser. No. 13/540,218 filed Jul. 2, 2012 and now issued asU.S. Pat. No. 8,788,066, which is a continuation of application Ser. No.13/286,169, filed Oct. 31, 2011 and now issued as U.S. Pat. No.8,437,867, which claims the benefit of Provisional Application Nos.61/408,421, filed Oct. 29, 2010, and 61/515,015, filed Aug. 4, 2011, thedisclosures of which are hereby incorporated by reference in theirentireties.

FIELD OF THE INVENTION

The present invention relates generally to baroreflex activation therapydevices and methods, and more particularly to an improved electrodedesign for use with an implant tool and procedure, as part of abaroreflex activation therapy system.

BACKGROUND OF THE INVENTION

Cardiovascular disease is a major contributor to patient illness andmortality. It also is a primary driver of health care expenditure,costing billions of dollars each year in the United States. Heartfailure is the final common expression of a variety of cardiovasculardisorders, including ischemic heart disease. It is characterized by aninability of the heart to pump enough blood to meet the body's needs andresults in fatigue, reduced exercise capacity and poor survival. Heartfailure results in the activation of a number of body systems tocompensate for the heart's inability to pump sufficient blood. Many ofthese responses are mediated by an increase in the level of activationof the sympathetic nervous system, as well as by activation of multipleother neurohormonal responses. Generally speaking, this sympatheticnervous system activation signals the heart to increase heart rate andforce of contraction to increase the cardiac output; it signals thekidneys to expand the blood volume by retaining sodium and water; and itsignals the arterioles to constrict to elevate the blood pressure. Thecardiac, renal and vascular responses increase the workload of theheart, further accelerating myocardial damage and exacerbating the heartfailure state. Accordingly, it is desirable to reduce the level ofsympathetic nervous system activation in order to stop or at leastminimize this vicious cycle and thereby treat or manage the heartfailure.

Hypertension, or high blood pressure, is a major cardiovascular disorderthat is estimated to affect 65 million people in the United Statesalone. Hypertension occurs when the body's smaller blood vessels(arterioles) constrict, causing an increase in blood pressure. Becausethe blood vessels constrict, the heart must work harder to maintainblood flow at the higher pressures. Although the body may tolerate shortperiods of increased blood pressure, sustained hypertension mayeventually result in damage to multiple body organs, including thekidneys, brain, eyes and other tissues, causing a variety of maladiesassociated therewith. The elevated blood pressure may also damage thelining of the blood vessels, accelerating the process of atherosclerosisand increasing the likelihood that a blood clot may develop. This couldlead to a heart attack and/or stroke. Sustained high blood pressure mayeventually result in an enlarged and damaged heart (hypertrophy), whichmay lead to heart failure.

Hypertension is a leading cause of heart failure and stroke, is theprimary cause of death for tens of thousands of patients per year, andis listed as a primary or contributing cause of death for hundreds ofthousands of patients per year in the U.S. Accordingly, hypertension isa serious health problem demanding significant research and developmentfor the treatment thereof. Hypertension remains a significant risk forpatients and challenge for health care providers around the worlddespite improvements in awareness, prevention, treatment and controlover the last 30 years. Patients with hypertension are encouraged toimplement lifestyle modifications including weight reduction, adoptingthe DASH eating plan, reducing dietary sodium, increasing physicalactivity, and limiting alcohol consumption and smoking. A large numberof pharmacologic treatments are also currently available to treathypertension.

An early attempt at treating hypertension first examined in the 1960'sand 1970's involved electrically stimulating the carotid sinus nerve.This therapy never gained widespread acceptance, likely due to thesimultaneous development of improved pharmacological agents for treatinghypertension, limitations associated with battery technology at thetime, and surgical limitations relating to isolating and placingelectrodes on the carotid sinus nerve. Furthermore, carotid sinus nervestimulation can negatively affect the patient's breathing patterns aswell as blood circulation. The paucity of literature on carotid sinusnerve stimulation during time is reflective of this and the lack of anysimilar or alternate stimulation systems for the treatment of drugresistant hypertension.

Recently, an improved approach for treating hypertension, heart failureand/or other cardiovascular disorders has been developed. BaroreflexActivation Therapy (“BAT”) utilizes electrical, mechanical, chemical,and/or other means of stimulation to activate one or more components ofa patient's baroreflex system, such as baroreceptors.

Baroreceptors are sensory nerve ends that are profusely distributedwithin the arterial walls of the major arteries, as well in the heart,aortic arch, carotid sinus or arteries, and in the low-pressure side ofthe vasculature such as the pulmonary artery and vena cava. Baroreceptorsignals are used to activate a number of body systems which collectivelymay be referred to as the baroreflex system. Baroreceptors are connectedto the brain via the nervous system, allowing the brain to detectchanges in blood pressure, which is indicative of cardiac output. Ifcardiac output is insufficient to meet demand (i.e., the heart is unableto pump sufficient blood), the baroreflex system activates a number ofbody systems, including the heart, kidneys, vessels, and otherorgans/tissues. Such natural activation of the baroreflex systemgenerally corresponds to an increase in neurohormonal activity.Specifically, the baroreflex system initiates a neurohormonal sequencethat signals the heart to increase heart rate and increase contractionforce in order to increase cardiac output, signals the kidneys toincrease blood volume by retaining sodium and water, and signals thevessels to constrict to elevate blood pressure. The cardiac, renal andvascular responses increase blood pressure and cardiac output, and thusincrease the workload of the heart. In a patient suffering from heartfailure, this further accelerates myocardial damage and exacerbates theheart failure state.

One of the first descriptions of treating hypertension throughbaroreceptor stimulation appears in U.S. Pat. No. 6,522,926 to Kieval etal., which discloses devices and methods for stimulating or activatingbaroreceptors or the baroreflex system to regulate blood pressure and/ortreat other cardiovascular disorders. Generally speaking, a baroreceptoractivation device may be activated, deactivated or otherwise modulatedto activate one or more baroreceptors and induce a baroreceptor signalor a change in the baroreceptor signal to thereby affect a change in thebaroreflex system. The baroreceptor activation device may be activated,deactivated, or otherwise modulated continuously, periodically, orepisodically. The baroreceptor activation device may utilize electricalas well as mechanical, thermal, chemical, biological, or a combinationthereof to activate the baroreceptor. The baroreceptor may be activateddirectly, or activated indirectly via the adjacent vascular tissue.Activation of this reflex increases afferent electrical signals throughthe carotid sinus nerve (Hering's nerve, a branch of theglossopharyngeal nerve, cranial nerve IX) to the medullary brain centersthat regulate autonomic tone. Increased afferent signals to thesemedullary centers cause a reduction in sympathetic tone and an increasein parasympathetic tone. This results in lower heart rate, reducedsodium and water reabsorption by the kidney resulting in a diuresis,relaxation of the smooth muscle in the blood vessels which results invasodilatation and a reduction in blood pressure. Thus, peripheralactivation of the baroreflex results in a physiologic response wherebyblood pressure is controlled by mechanisms determined by the integrativeaction of the central nervous system action on all peripheral organs andblood vessels.

The process of implanting a baroreflex activation device for deliveringbaroreflex therapy, such as an electrode assembly, involves positioningthe assembly such that the electrodes are properly situated against thearterial wall of the carotid sinus, and securing the electrode assemblyto the artery so that the positioning is maintained. The process ofadjusting and re-adjusting the position of the electrode assembly duringimplantation, known as mapping, adds to the overall procedure time.Present-day procedures involve positioning and holding the electrodeassembly in place with forceps, hemostat or similar tool while applyingthe stimulus and observing the response in the patient. Movement by aslittle as 1 mm can make a medically relevant difference in theeffectiveness of the baroreceptor activation.

One example of mapping methods and techniques for implanting electrodesis disclosed in U.S. Pat. No. 6,850,801 to Kieval et al. The positioningis a critical step, as the electrodes must direct as much energy aspossible toward the baroreceptors for maximum effectiveness andefficiency. The energy source for the implanted baroreflex stimulationdevice is typically an on-board battery with finite capacity, and it isdesirable to provide a lower energy source to ensure patient safety. Ahigh-efficiency implantation will provide a longer battery life andcorrespondingly longer effective service life between surgeries becauseless energy will be required to achieve the needed degree of therapy. Assuch, during implantation of the electrode assembly, the position of theassembly is typically adjusted several times during the implantationprocedure in order to optimize the baroreflex response.

Another challenge related to the positioning process is the task ofkeeping track of previous desirable positions. Because positioning theelectrode assembly is an optimization procedure, surgeons will tend tosearch for better positions until they have exhausted all reasonablealternative positions. Returning the electrode assembly to apreviously-observed optimal position can be quite difficult andfrustrating, especially under surgical conditions. Additionally,previous mapping approaches required large incisions to provideclearance for positioning and re-positioning of the electrode assembly.

SUMMARY OF THE INVENTION

Devices and methods of use for introduction and implantation of anelectrode as part of a minimally invasive technique. An implantablebaroreflex activation system includes a control system having animplantable housing, an electrical lead, attachable to the controlsystem, and an electrode structure. The electrode structure is near oneend of the electrical lead, and includes a monopolar electrode, abacking material having an effective surface area larger than theelectrode, and a releasable pivotable interface to mate with an implanttool. The electrode is configured for implantation on an outer surfaceof a blood vessel and the control system is programmed to deliver abaroreflex therapy via the monopolar electrode to a baroreceptor withina wall of the blood vessel.

A method of implanting a baroreflex activation system includes creatingan incision in a patient and releasably coupling an electrode structureto an implant tool, the electrode structure including a monopolarelectrode, a backing material having an effective surface area largerthan the monopolar electrode, and a means for releasably and pivotablyinterfacing with the implant tool. The method further includesdetermining a suitable implant location for the electrode structure on ablood vessel by manipulating the implant tool within the incision,securing the electrode structure at the implant location such that themonopolar electrode is in contact with an outer surface of the bloodvessel, implanting the housing, and connecting the electrode structureto the control system with the electrical lead.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, in which:

FIG. 1 is a cross-sectional schematic illustration of baroreceptorswithin the vascular wall and the baroreflex system.

FIG. 2 is a schematic illustration of a baroreceptor activation systemin accordance with the present invention.

FIG. 3A is a plan view of an electrode coupled with a lead according toan embodiment of the present invention.

FIG. 3B is a close-up inverted view of a portion of FIG. 3A.

FIG. 4A is an isometric view of an implant tool according to anembodiment of the present invention.

FIG. 4B is a close-up plan view of the interface tip of the implant toolof FIG. 4A.

FIG. 4C is a close-up plan view of the implant tool of FIG. 4A coupledwith an electrode.

FIG. 5A is an elevation view of an implant tool according to anotherembodiment of the present invention.

FIG. 5B is a close-up elevation view of a portion of FIG. 5A.

FIG. 6A is an isometric view of the implant tool of FIG. 5A positionedproximate an electrode structure according to an embodiment of thepresent invention.

FIG. 6B is an isometric view of the implant tool of FIG. 6A engaged withthe electrode structure.

FIG. 7A is a schematic representation of an electrode structure beingimplanted on a blood vessel with the use of an implant tool, accordingto an embodiment of the present invention.

FIG. 7B is a schematic representation of the electrode structure of FIG.7A fixed in place on the blood vessel.

FIGS. 8A and 8B are a schematic representations of a baroreflexactivation system according to an embodiment of the present inventionimplanted on a carotid sinus within a patient.

FIG. 9A is a plan view of the tissue contact side of an electrodestructure according to an embodiment of the present invention.

FIG. 9B is a perspective view of a fixation member according to anembodiment of the present invention.

FIGS. 10A-10E are perspective views of related electrode structureconfigurations according to embodiments of the present invention.

FIG. 11A is an isometric view of an electrode structure and fixationmechanism according to an embodiment of the present invention.

FIG. 11B is an elevation view of an implant tool according to anotherembodiment of the present invention for use with the electrodearrangement of FIG. 11A.

FIG. 11C is a close-up plan view of the electrode structure of FIG. 11Aheld in an open, retracted position by the implant tool of FIG. 11B.

FIG. 12A is a perspective view of an implant tool according to anotherembodiment of the present invention.

FIG. 12B is a perspective view of a fixation element for use with anelectrode structure according to an embodiment of the present invention.

FIG. 13A is a table of operating parameters during an experimentdescribed herein.

FIG. 13B is a graph depicting the results of the experiment describedherein.

FIG. 14 is a schematic representation of a kit according to anembodiment of the present invention.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It should be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

The following detailed description should be read with reference to thedrawings in which similar elements in different drawings are numberedthe same. The drawings, which are not necessarily to scale, depictillustrative embodiments and are not intended to limit the scope of theinvention.

To address the problems of hypertension, heart failure, othercardiovascular disorders and renal disorders, the present inventionbasically provides a number of devices, systems and methods by which thebaroreflex system is activated to reduce excessive blood pressure,autonomic nervous system activity and neurohormonal activation. Inparticular, the present invention provides a number of devices, systemsand methods by which baroreceptors may be activated, thereby indicatingan increase in blood pressure and signaling the brain to reduce thebody's blood pressure and level of sympathetic nervous system andneurohormonal activation, and increase parasympathetic nervous systemactivation, thus having a beneficial effect on the cardiovascular systemand other body systems.

For general information pertaining to the cardiovascular, circulatoryand nervous systems, as well as baroreceptor and baroreflex therapysystems that may be used in whole or in part with embodiments of thepresent invention, reference is made to the following commonly assignedpatent applications and patents: Published U.S. Patent Application Nos.2006/0004417 to Rossing et al. and 2006/0074453 to Kieval et al., andU.S. Pat. No. 6,522,926 to Kieval et al., U.S. Pat. No. 6,850,801 toKieval et al., U.S. Pat. No. 6,985,774 to Kieval et al., U.S. Pat. No.7,480,532 to Kieval et al., U.S. Pat. No. 7,499,747 to Kieval et al.,U.S. Pat. No. 7,835,797 to Rossing et al., U.S. Pat. No. 7,840,271 toKieval et al., U.S. Pat. No. 8,086,314 to Kieval, U.S. Pat. No.8,620,422 to Kieval et al., the disclosures of which are herebyincorporated by reference in their entireties except for the claims andany express definitions.

Refer now to FIG. 1, which depicts a schematic illustration ofbaroreceptors 30 disposed in a generic vascular wall 40 and a schematicflow chart of the baroreflex system 50. Baroreceptors 30 are profuselydistributed within the vascular walls discussed previously, andgenerally form an arbor 32. The baroreceptor arbor 32 comprises aplurality of baroreceptors 30, each of which transmits baroreceptorsignals to the brain 52 via nerve 38. The baroreceptors 30 are soprofusely distributed and arborized within the vascular wall 40 thatdiscrete baroreceptor arbors 32 are not readily discernable. To thisend, those skilled in the art will appreciate that the baroreceptors 30depicted in FIG. 1 are primarily schematic for purposes of illustrationand discussion.

Baroreceptor signals in the arterial vasculature are used to activate anumber of body systems which collectively may be referred to as thebaroreflex system. For the purposes of the present invention, it will beassumed that the “receptors” in the venous and cardiopulmonaryvasculature and heart chambers function analogously to the baroreceptorsin the arterial vasculature, but such assumption is not intended tolimit the present invention in any way. In particular, the methodsdescribed herein will function and achieve at least some of the statedtherapeutic objectives regardless of the precise and actual mechanismresponsible for the result. Moreover, the present invention may activatebaroreceptors, mechanoreceptors, pressoreceptors, stretch receptors,chemoreceptors, or any other venous, heart, or cardiopulmonary receptorswhich affect the blood pressure, nervous system activity, andneurohormonal activity in a manner analogous to baroreceptors in thearterial vasculation. For convenience, all such venous receptors will bereferred to collectively herein as “baroreceptors” or “receptors” unlessotherwise expressly noted.

While there may be small structural or anatomical differences amongvarious receptors in the vasculature, for the purposes of someembodiments of the present invention, activation may be directed at anyof these receptors and/or nerves and/or nerve endings from thesereceptors so long as they provide the desired effects. In particular,such receptors will provide afferent signals, i.e., signals to thebrain, which provide the blood pressure and/or volume information to thebrain. This allows the brain to cause “reflex” changes in the autonomicnervous system, which in turn modulate organ activity to maintaindesired hemodynamics and organ perfusion. Stimulation of the baroreflexsystem may be accomplished by stimulating such receptors, nerves, nervefibers, or nerve endings, or any combination thereof.

A baroreflex activation therapy system utilizing an improved electrodeand lead arrangement according to embodiments of the present inventiongenerally include a control system, a baroreceptor activation device, alead and a sensor (optional). Referring now to FIG. 2, one embodiment ofa system for baroreflex therapy is depicted, including a control system60, a baroreflex activation device 70, and one or more sensor(s) 80. Thecontrol system 60 may include a therapy block 61 comprising a processor63 and a memory 62. Control system 60 is enclosed within a housing, orcan, and is communicably coupled to baroreflex activation device 70 suchas by way of electric control cable 72, or by wireless means such asradiofrequency or other forms of wireless communication. Cable 72 mayinclude an optional attachment tab 73, which may be used to suture orotherwise attach cable 72 to a patient in order to provide strain reliefto the electrode-tissue interface. Control system 60 includes a driver66 to provide the desired power mode for the baroreceptor activationdevice 70. For example if the baroreceptor activation device 70 utilizeselectrical actuation, the driver 66 may comprise a power amplifier,pulse generator or the like to selectively deliver electrical controlsignals, and the cable 72 may comprise electrical lead(s).

The electrical control signal generated by the driver 66 may becontinuous, periodic, episodic or a combination thereof, as dictated byan algorithm contained in memory 62 of the control system 60. Continuouscontrol signals include a constant pulse, a constant train of pulses, atriggered pulse and a triggered train of pulses. Periodic controlsignals include each of the continuous control signals described abovewhich have a designated start time and a designated duration. Episodiccontrol signals include each of the continuous control signals describedabove which are triggered by an episode.

The control system memory 62 may contain data related to the sensorsignal, the therapy signal, and/or values and commands provided by theinput device 64. The memory 62 may also include software containing oneor more algorithms defining one or more functions or relationshipsbetween the therapy signal and the sensor signal. The algorithm maydictate activation or deactivation therapy signals depending on thesensor signal or a mathematical derivative thereof. The algorithm maydictate an activation or deactivation therapy signal when the sensorsignal falls below a lower predetermined threshold value, rises above anupper predetermined threshold value or when the sensor signal indicatesa specific physiologic event. The memory 62 may also include softwarecontaining one or more algorithms for determining patient physiologicalparameters based on a measured parameter.

In one embodiment, the sensor(s) 80 senses and/or monitors a parameter,and generates a signal indicative of the parameter. The parameter may berelated to cardiovascular function, and/or indicative of a need tomodify the baroreflex system, and/or a physical parameter such asvascular impedance. The control system 60 receives the sensor signalfrom sensor 80 and transmits the therapy signal to the baroreflexactivation device 70 by way of control cable 72. The sensor 80 may becombined and/or integrated with baroreflex activation device 70, e.g.,an electrode having sensing and therapy capabilities, or sensor 80 maybe separate from baroreflex activation device 70 and communicablycoupled to control system 60.

The control system 60 generates a control signal (also referred to as atherapy signal), which activates, deactivates or otherwise modulates thebaroreflex activation device 70. In one embodiment, the therapy signalis in the range of about 1 to 10 volts, at a rate between 5 Hz and 200Hz. Typically, activation of the device 70 results in activation of thebaroreceptors 30. Alternatively, deactivation or modulation of thebaroreflex activation device 70 may cause or modify activation of thebaroreceptors 30. The baroreflex activation device 70 may include a widevariety of devices which utilize electrical means, such as electrodes,to activate baroreceptors 30.

The control system 60 may operate as a closed loop utilizing feedbackfrom the sensor 80, and optionally other sensors, such as heart ratesensors, which may be incorporated, or as an open loop utilizingreprogramming commands received by input device 64. The closed loopoperation of the control system 60 preferably utilizes some feedbackfrom the sensor(s), but may also operate in an open loop mode withoutfeedback. In a closed loop embodiment, control system 60 generates acontrol signal as a function of the signal received from sensor 80.Thus, in one embodiment when sensor 80 detects a parameter indicative ofthe need to modify the baroreflex system activity (e.g., excessive bloodpressure), the control system 60 generates a therapy signal to modulate(e.g., activate) the baroreflex activation device 70 thereby inducing abaroreceptor 30 signal that is perceived by the brain 52 to be apparentexcessive blood pressure. When the sensor 80 detects a parameterindicative of normal body function (e.g., normal blood pressure), thecontrol system 60 generates a therapy signal to modulate (e.g.,deactivate) the baroreflex activation device 70.

Programming commands received by the input device 64 may directlyinfluence the therapy signal, the output activation parameters, or mayalter the software and related algorithms contained in memory 62. Thetreating physician and/or patient may provide commands to input device64. In one embodiment, a display 65 may be used to view the sensorsignal, therapy signal and/or the software/data contained in memory 62.Control system 60 may be implanted in whole or in part.

In one embodiment, baroreceptor activation device 70 comprises anelectrode structure 110. Electrode structure 110 generally includes anelectrode 112 mounted on, integrated with, or otherwise coupled to abacker 114. Electrode 112 may comprise platinum iridium, and may includea surface treatment, such as iridium oxide or titanium nitride and/orcan include steroid, anti-inflammatory, antibiotic and/or analgesiccompounds, for example. Backer 114 may be constructed ofDacron-reinforced insulated silicone, or other suitable materials thatare flexible, sturdy, electrically insulative and/or suitable forimplantation in a body. Backer 114 and/or electrode 112 may comprisecircular structures, or other suitable arrangements without departingfrom the spirit of the invention. For example backer 114 may include oneor more tabs or features configured for facilitating fixation to tissue.In one embodiment, electrode 112 may have a diameter of about 1 mm, andbacker 114 may have a diameter of about 6 mm. However, it iscontemplated that electrode 112 may have a diameter within a range ofabout 0.25 mm-3 mm, while backer 114 may have a diameter within a rangeof about 1 mm-10 mm. In one embodiment the diameter of backer 114 is atleast twice the diameter of electrode 112.

Electrode 112 comprises a cathode, and in one embodiment the housing ofcontrol system 60 may comprise an anode. In another embodiment, an anodemay be provided as part of lead 72. In another embodiment, an anode isprovided on a second lead which is also coupled to control system 60. Inall embodiments the anode is preferably sufficiently larger than thecathode, for example ten times larger. In another embodiment the anodeis fifty times larger than the cathode. Further, the anode and cathodeare preferably positioned at a minimum distance away from one another,for example, the distance may be about twenty times the cathodediameter. In another embodiment, the distance between anode and cathodeis at least fifty times the cathode diameter.

One or more electrode structures 110 may be provided as part of abaroreflex activation therapy system according to the present invention.For example, a first electrode structure 110 may be positioned at afirst anatomical location, while a second electrode structure 110 ispositioned at a second anatomical location, such as for example at aleft carotid sinus and a right carotid sinus. Or a first electrodestructure 110 may be positioned at a first anatomical location while asecond electrode structure is positioned at a second anatomical locationproximate the first anatomical location, such as for example positioningfirst and second electrode structures proximate one another on the leftcarotid sinus and/or carotid arteries.

Electrode structure 110 may also include an interface means 120configured for coupling with an implant tool, and one or more fixationmeans 122. Preferably interface means 120 is included on the inactiveside of electrode structure 110. As described herein, interface means(or attachment interface) may comprise a t-bar, a socket, or otherstructure capable of being coupled to or grasped by an implant tool.Referring now to FIGS. 3A-4C, electrode structure 110 includes aninterface means 120 in the form of t-bar 130 which includes a barportion 132 raised above the inactive side of electrode structure 110.T-bar 130 is configured to interface with an implant tool 134, whichgenerally includes a body portion 136 and an interface tip 138. Bodyportion 136 of tool 134 may be generally rigid, or may include aninternal wire or coil to allow tool 134 to be bent or curved and retainthe curved shape. Body portion 136 may also include a telescoping orsimilar arrangement to provide adjustability of the overall length oftool 134. Interface tip 138 may similarly include a telescoping orsimilar arrangement, separate from that of the body portion. One or morepivot points may also be provided on tool 134, such as between tip 138and body portion 136, or at any desired location along body 136. Tipportion 138 includes a cradle 139 configured to releasably couple tot-bar 130, while allowing tool 134 to pivot, rotate, and/or otherwiseprovide freedom of movement about t-bar 130 to facilitate movingelectrode structure 110 around the curved surface of an implant locationsuch as the outer surface of a blood vessel 40, as part of a mappingand/or implant procedure.

In another embodiment depicted in FIGS. 5A-7A, interface means 120comprises a socket 150 disposed on the inactive side of electrodestructure 110. Socket 150 is configured to interface with an implanttool 154, which generally includes a body portion 156 and an interfacetip 158. Body portion 156 of tool 154 may be generally rigid, or mayinclude an internal coil or wire to allow tool 154 to be bent or curvedand retain the curved shape. Body portion 156 may also include atelescoping or similar arrangement to provide adjustability of theoverall length of tool 154. Interface tip 158 may similarly include atelescoping or similar arrangement, separate from that of the bodyportion. One or more pivot points may also be provided on tool 154, suchas between tip 158 and body portion 156, or at any desired locationalong body 156. Tip portion 158 includes a ball end 159 configured toreleasably couple to socket 150 of electrode structure 110. Theball-and-socket arrangement provides a wide range of motion aboutmultiple axes between electrode structure 110 and implant tool 154 tofacilitate moving electrode structure 110 around the curved surface ofan implant location such as the outer surface of a blood vessel 40, aspart of a mapping and/or implant procedure. This articulatedball-and-socket joint preferably provides at least three degrees offreedom: pitch, yaw and roll. Further, the ball-and-socket jointpreferably provides a range of motion of up to 150 degrees in at leasttwo separate axes.

In order to implant electrode structure 110, a surgeon first identifiesand marks the desired implant location. Without limitation, one exampleof a suitable site for delivering baroreflex activation therapy is thecarotid sinus. The general implant location may be obtained with the useof ultrasound, or other imaging techniques known and available. A smallincision is made on the patient in the identified region. The length ofthe incision should be less than four inches long, preferably less thantwo inches. The size of the incision needed will be determined by thelocation of the implant and the specific patient, however the electrodestructure 110 and implant tool embodiments described herein allow forthe use of a minimally invasive incision as compared to implantprocedures for previous baroreflex activation devices.

Determining an optimal location to affix electrode structure 110 iscritical for effective therapy, and a mapping procedure is thereforeundertaken. Electrode structure 110 is releasably coupled to the implanttool, and introduced into the incision until electrode structure 110 isin contact with the implant site, such as for example the carotid sinus.A stimulation signal is provided to electrode structure 110, such asfrom an external pulse generator, and one or more patient responses tothe signal is then measured. Using the implant tool, electrode structure110 is moved around the contours of the carotid sinus to differentpositions, with additional stimulation signals delivered and patientresponses measured at each position. When the surgeon has located anoptimal site for implantation, electrode structure 110 is fixed at thesite. The implant tool is then removed.

A path may be tunneled for lead 72 from the electrode implant locationto the implant location of control system 60 housing. This path may betunneled either before or after the mapping procedure. If lead 72includes a strain relief attachment tab 73, the tab is then sutured inplace near electrode structure 110. The control system housing is thenimplanted subcutaneously as known in the art, and the lead is attached.FIGS. 8A-8B are schematic illustrations of the baroreflex activationsystem fully implanted.

Numerous fixation means and techniques are provided for securingelectrode structure 110 to an implant site, and may include passive oractive fixation. Electrode structure 110 may be sutured directly to ablood vessel, and backer 114 may optionally include one or moreapertures 123 as depicted in FIG. 9A, to facilitate a path for suturesthrough backer 114. Preferably at least two sutures are utilized toinsure electrode structure 110 is secure and in sufficient electricalcontact with the blood vessel.

Another embodiment of a fixation means 122 for electrode structure 110,depicted in FIG. 9B, is a U-Clip technique utilizing self-closingnitinol U-Clip components. U-clips 124 (such as those produced byMedtronic, Inc. of Minneapolis, Minn.) can be used to secure electrodestructure 110, and are placed in the same positions as sutures. A sutureneedle is brought through the tissue to the location of the U-clip (onthe end). The surgeon cuts the suture thread at the end nearest theU-clip and the U-clip assumes the deployed position. In someembodiments, an “off the shelf” U-clip as described above may have to bemodified to use the correct number of connection points and to be thecorrect size and shape (such as by making them circular) to match backer114.

In a further embodiment depicted in FIGS. 10A-10E, fixation of electrodestructure 110 is accomplished in whole or in part with the use ofadhesives. Backer 114 may include one or more features to facilitateapplication of an adhesive, such as apertures 182, troughs 184, and/ortabs 186. Backer 114 may further include a perforated polyester mesh 188strategically exposed to provide additional surface area to mate withthe adhesive. Suitable adhesives include known medical adhesives such asCryolife bioglue, acrylic-based adhesives or photo-activated adhesives.Anti-inflammatory and/or anti-scarring agents may be used in conjunctionwith an adhesive. Further, adhesive fixation be used in combination withother fixation means described herein.

In another embodiment depicted in FIGS. 11A-11C, electrode structure 110includes an integrated, selectively deployable active fixation element160 which generally includes a frame portion 162 and a plurality offixation barbs 164. Fixation element 160 is coupled to electrodestructure 110, and may be constructed of shape-memory alloy such asnitinol, or other suitable materials. An implant tool 170 is providedfor mapping and implant of electrode structure 110, and generallyincludes a body portion 171 having a grasping means 172 at a distal endand a control means 173 at a proximal end. Control means 173 may bemanipulated by a surgeon to cause grasping means 172 to hold frameportion 162 in a retracted position wherein fixation barbs 164 areretracted, thereby allowing introduction of electrode structure 110 tothe implant site. A mapping procedure as described above may be carriedout, and upon finding a satisfactory implant location, control means 173is manipulated to cause grasping means 172 to release frame 162 and movefixation element 160 to a deployed position, allowing barbs 164 topenetrate into the adventitia of a blood vessel and securing electrodestructure 110.

In an alternate embodiment depicted in FIGS. 12A-12B, fixation element160 is deployed via a rotational approach. A plurality of barbs 164 areincluded on a frame 162, which is coupled to an electrode structure 110.Barbs 164 may be pre-formed to have a helix-like curvature. Whenretained by implant tool 140, barbs 164 are withdrawn into implant tool140 or otherwise held in a retracted position as to allow forintroduction of electrode structure 110 to the implant site and formapping. When desired, implant tool 140 is manipulated to cause graspingmeans to rotatably deploy fixation element 162.

Referring now to operation of a baroreflex therapy system according tothe present invention, as mentioned above the control signal generatedby the control system 60 may be continuous, periodic, episodic or acombination thereof, as dictated by an algorithm contained in memory 62.The algorithm contained in memory 62 defines a stimulus regimen whichdictates the characteristics of the control signal as a function oftime, and thus dictates the stimulation of baroreceptors as a functionof time. Continuous control signals include a pulse, a train of pulses,a triggered pulse and a triggered train of pulses, all of which aregenerated continuously.

The output (power or energy) level of the baroreceptor activation device70 may be altered by changing the voltage, current and/or signalduration. The output signal of the baroreceptor activation device 70 maybe, for example, constant current or constant voltage. In electricalactivation embodiments using a modulated signal, wherein the outputsignal comprises, for example, a series of pulses, several pulsecharacteristics may be changed individually or in combination to changethe power or energy level of the output signal. Such pulsecharacteristics include, but are not limited to: pulse amplitude (PA),pulse frequency (PF), pulse width or duration (PW), pulse waveform(square, triangular, sinusoidal, etc.), pulse polarity (for bipolarelectrodes) and pulse phase (monophasic, biphasic).

In electrical activation embodiments wherein the output signal comprisesa pulse train, several other signal characteristics may be changed inaddition to the pulse characteristics described above. The control oroutput signal may comprise a pulse train which generally includes aseries of pulses occurring in bursts. Pulse train characteristics whichmay be changed include, but are not limited to: burst amplitude (equalto pulse amplitude if constant within burst packet), burst waveform(i.e., pulse amplitude variation within burst packet), burst frequency(BF), and burst width or duration (BW). The signal or a portion thereof(e.g., burst within the pulse train) may be triggered by any of theevents discussed previously, or by a particular portion of the arterialpressure signal or the ECG signal (e.g., R-wave), or another physiologictiming indicator. If the signal or a portion thereof is triggered, thetriggering event may be changed and/or the delay from the triggeringevent may be changed.

Control signal characteristics for a baroreflex therapy system having amonpolar electrode 110 according to the present invention differ fromprior approaches, and provide greater stimulation efficacy with a lowerpower consumption. For example, suitable pulse widths for the presentinvention are in the range of about 15 microseconds to 500 microseconds,preferably in the range of 60-200 microseconds, and more preferably inthe range of 100-150 microseconds. Suitable pulse amplitudes are in therange of about 0.4-20 milliamps, preferably in the range of 3-10milliamps, and more preferably in the range of 5-7 milliamps. Suitablepulse frequencies are in the range of about 10-100 Hz, preferably in therange of 25-80 Hz, and more preferably in the range of 40-70 Hz.

A number of human patients were implanted with baroreflex activationtherapy systems according to the embodiments described herein. Thesepatients had systolic blood pressures in excess of 140 mmHg despite theusage of at least three anti-hypertensive medications. The results oftheir first five months being implanted with the system are presented inFIGS. 13A-13B, which depict the average operating parameters for thesystem and the average resulting blood pressure reduction. These resultsillustrate that therapy delivered in accordance with the embodimentsdescribed herein resulted in a significant reduction in blood pressureof the patient.

Referring now to FIG. 14, in one embodiment a baroreflex therapy systemcan be provided to a user in a kit 200. Kit 200 may include a controlsystem 60 in a housing, a baroreflex activation device 70 having atleast one electrode structure 110 and coupled to the control system, anoptional sensor, an optional implant tool 202, and a set of instructions210 recorded on a tangible medium for implanting, programming and/oroperating the system. Kit 200 may be comprised of one or morehermetically sealed and sterilized packages. Instructions 210 may beprovided as part of kit 200, or indications may be provided linking auser to electrically accessible instructions 210. Instructions 210 mayinclude instructions for implanting electrode structure 110 and thebaroreflex activation therapy system as described herein including theuse of an implant tool and/or a mapping procedure, and/or forprogramming and/or operating control system 60.

Various modifications to the embodiments of the inventions may beapparent to one of skill in the art upon reading this disclosure. Forexample, persons of ordinary skill in the relevant art will recognizethat the various features described for the different embodiments of theinventions can be suitably combined, un-combined, and re-combined withother features, alone, or in different combinations, within the spiritof the invention. Likewise, the various features described above shouldall be regarded as example embodiments, rather than limitations to thescope or spirit of the inventions. Therefore, the above is notcontemplated to limit the scope of the present inventions.

Persons of ordinary skill in the relevant arts will recognize that theinventions may comprise fewer features than illustrated in anyindividual embodiment described above. The embodiments described hereinare not meant to be an exhaustive presentation of the ways in which thevarious features of the inventions may be combined. Accordingly, theembodiments are not mutually exclusive combinations of features; rather,the inventions may comprise a combination of different individualfeatures selected from different individual embodiments, as understoodby persons of ordinary skill in the art.

Any incorporation by reference of documents above is limited such thatno subject matter is incorporated that is contrary to the explicitdisclosure herein. Any incorporation by reference of documents above isfurther limited such that no claims included in the documents areincorporated by reference herein. Any incorporation by reference ofdocuments above is yet further limited such that any definitionsprovided in the documents are not incorporated by reference hereinunless expressly included herein.

For purposes of interpreting the claims for the embodiments of thepresent inventions, it is expressly intended that the provisions ofSection 112, sixth paragraph of 35 U.S.C. are not to be invoked unlessthe specific terms “means for” or “step for” are recited in a claim.

The invention claimed is:
 1. An implantable electrode structure for use in a baroreflex activation system, the implantable electrode structure configured for fixation on an outer surface of a blood vessel such as a carotid sinus, the electrode structure comprising: a first backing material layer configured to be placed in contact with the blood vessel; a solid electrode disposed on the first backing layer; a second backing material layer; and a mesh layer disposed between the first backing material layer and the second backing material layer, wherein at least one of the first backing material layer and the second backing material layer includes at least one aperture that exposes the mesh layer, the mesh layer being exposed to provide additional surface area to allow fixation of the electrode structure to the blood vessel, wherein at least one of the first backing material layer and the second backing material layer has a surface area larger than the electrode, wherein the electrode structure is sized and configured to extend around less than half of a circumference of the blood vessel when implanted.
 2. The implantable electrode structure of claim 1, wherein the electrode structure has a plurality of apertures each with edges at which the mesh layer is exposed.
 3. The implantable electrode structure of claim 1, wherein the mesh extends outwardly of at least one of the first backing material layer and the second backing material layer.
 4. The implantable electrode structure of claim 1, wherein the mesh extends outwardly of at least one of the first backing material layer and the second backing material layer and has a trough for use of an adhesive to aid fixation.
 5. The implantable electrode structure of claim 1, wherein the mesh has tabs which extend outwardly of at least one of the first backing material layer and the second backing material layer.
 6. The implantable electrode structure of claim 1, wherein the at least one aperture is disposed inwardly of an outer perimeter of the implantable electrode structure.
 7. The implantable electrode structure of claim 1, wherein the at least one aperture extends through the second backing material layer, the mesh layer and the first backing material layer.
 8. The implantable electrode structure of claim 1, wherein the implantable electrode structure is generally circular.
 9. The implantable electrode structure of claim 1, wherein at least one of the first backing material layer and the second backing material layer has apertures and wherein the mesh is exposed through the apertures.
 10. The implantable electrode structure of claim 1, wherein the electrode is arranged generally in the center of the electrode structure.
 11. The implantable electrode structure of claim 1, wherein at least one of the first backing material layer and the second backing material layer has a diameter of about six millimeters and the electrode has a diameter of about one millimeter.
 12. The implantable electrode structure of claim 1, wherein an area of the backing material is at least ten times greater than an area of the electrode.
 13. The implantable electrode structure of claim 1, wherein an area of at least one of the first backing material layer and the second backing material layer is at least thirty times greater than an area of the electrode.
 14. The implantable electrode structure of claim 1, wherein at least a portion of the mesh layer is exposed on the first backing material layer.
 15. The implantable electrode structure of claim 1, wherein the mesh is exposed around or through the second backing material layer.
 16. A method of providing an implantable electrode structure for use in a baroreflex activation system, the implantable electrode structure configured for fixation on an outer surface of a blood vessel such as a carotid sinus, the method comprising forming the implantable electrode structure by: providing a backing material having a first side and a second side; providing a mesh layer between the first side and the second side; mounting a solid electrode on the first side of the backing material, the electrode being configured to be placed in contact with the blood vessel; and exposing the mesh layer through an aperture on the second side to provide additional surface area to allow fixation of the electrode structure to the blood vessel, wherein the backing material has a surface area larger than the electrode, wherein the electrode structure is sized and configured to extend around less than half of a circumference of the blood vessel when implanted.
 17. The method of claim 16, further comprising exposing the mesh layer around or through the first side of the backing material.
 18. The method of claim 16, further comprising providing an aperture on the backing material, the mesh layer being exposed through the aperture.
 19. The method of claim 16, further comprising providing an aperture through the first side, the mesh layer and the second side.
 20. An implantable electrode structure for use in a baroreflex activation system, the implantable electrode structure configured for fixation on an outer surface of a blood vessel such as a carotid sinus, the electrode structure comprising: a first side having a solid electrode, the first side configured to be placed in contact with the blood vessel; a second side opposite the first side, the second side including a backing material having a surface area larger than the electrode, the backing material having an outer perimeter; a mesh layer, wherein the backing material includes at least one aperture that exposes the mesh layer through the backing material to the second side, the mesh layer being exposed to provide additional surface area to allow fixation of the electrode structure to the blood vessel, wherein the electrode structure is sized and configured to extend around less than half of a circumference of the blood vessel when implanted, wherein the backing material has a diameter of about six millimeters and the electrode has a diameter of about one millimeter. 